Micromirror systems with concealed multi-piece hinge structures

ABSTRACT

Micromirror systems with concealed multi-piece hinge structures are provided for reflective applications. Generally, light is reflected by these structures adapted for three-dimensional tilt as well as up-and-down or out-of-plane actuation. Devices can be produced utilizing the various optional features described herein to provide miniaturized, highly controllable solutions for use in optical switching, projection and other applications, especially optical applications.

FIELD OF THE INVENTION

The present invention relates generally to the field of spatial lightmodulators that can modify or correct an optical wavefront. Moreparticularly, the invention relates to micro electro-mechanical systems(MEMS) in the form of micromirror devices used in adaptive optics,optical switching applications, or other light manipulation applicationssuch as displays.

BACKGROUND OF THE INVENTION

MEMS devices are small structures, typically fabricated on asemiconductor wafer using processing techniques including opticallithography, metal sputtering or chemical vapor deposition, and plasmaetching or other etching techniques that have been developed for thefabrication of integrated circuits. Micromirror devices are a type ofMEMS device. Other types of MEMS devices include accelerometers,pressure and flow sensors, fuel injectors, inkjet ports, and gears andmotors, to name a few. Micromirror devices have already met with a greatamount of commercial success.

MEMS micromirror devices are being used in a variety of applications,including optical display systems, optical cross-connects for switchingof optical data signals and adaptive optics for phase and other types ofcorrection. One type of display device that has been used with a greatdeal of success is the Texas Instruments DLP™. In this system, manymirrors are operated individually in a bistable, digital fashion tocreate a projected display. Although current commercial technology hasbeen limited to about 1.3 million pixels in the mirror array, greatermirror densities and higher yields should improve this in the future asthe technology progresses.

Arrays of multi-axis tilting mirrors can also be found in otherapplications, such as beam steering, printing, scanning, and projection,among many. Most current arrays of micromirrors can be separated intotwo categories: relatively large single mirrors that steer a singlebeam, or arrays of smaller mirrors, where many mirrors aim each lightbeam.

Larger mirrors can offer some advantages when steering a smaller numberof discrete light beams in terms of providing an unbroken, nominallyflat surface with high reflectivity. However, if the beams are too largefor the mirrors, or if they are misaligned, the reflected beam isclipped and has less intensity. These types of arrays are less suitablefor reflecting larger, continuous light such as an optical image.Generally, the support structures between actuating mirror elementsleave too much space and thus create noticeable holes in the reflectedimage. Arrays of smaller mirrors also have drawbacks. Many currentdesigns may only move in one axis, which limits some of their potentialapplications. Others that can move in a multi-axis fashion also oftenhave relatively large gaps from one mirror to the next that affect thequality of the reflected beam or image. Micromirrors set in an arraysuch as this must have some gaps between them to allow full movement ofeach mirror, but it is advantageous to decrease the size of the gaps asmuch as possible. In addition, many designs have support structures thatare small, yet are part of the visible surface. These can alsocontribute to the spacing between mirrors. Supports and hinges that arehidden behind the mirror surface would improve the overall reflectivesurface area.

A particularly important application for multi-axis tilting micromirrorsis in the field of optical switching. A typical optical cross-connectfor an optical networking switch includes a switching matrix having twoarrays or clusters of MEMS micromirrors. The first array of micromirrorsis arranged so that micromirrors in the first array receive opticalinput signals from one or more input sources, such as optical fiberinput(s) and the second array of micromirrors is arranged so thatmicromirrors in the second array receive optical signals reflected frommicromirrors in the first array and direct the signals as optical outputsignals to one or more optical outputs.

The micromirrors in each array are capable of being adjusted, steered ortilted, so that a micromirror in the first array is capable of directinga reflected optical signal to a micromirror in the second array selectedfrom a plurality of the micromirrors in the second array. Similarly, themicromirrors in the second array can be adjusted, steered or tilted soas to align with a micromirror in the first array selected from aplurality of the micromirrors in the first array. Thus, by appropriateorientation of the micromirrors by adjustment, steering or tilting, afirst micromirror in the first array can be set to deliver an opticalsignal to a first, second, or third, etc. micromirror of the secondarray, as desired, and so forth, thereby providing the switchingcapability of the cross-connect.

The performance of optical cross-connects that use such arrangements ofMEMS micromirrors depends upon a number of factors, including how wellthe micromirrors in the first array are optically aligned with themicromirrors in the second array, changes in temperature, voltagedrifts, and performance of the mirror surfaces of the micromirrors,which are affected by the shape or flatness of the mirror surface. Evenunder the best circumstances, when the micromirrors in the first andsecond arrays are accurately aligned and the other factors mentionedabove are minimized, current cross-connects often lose 60% to 70% (about4-5 dB losses) of the light passing through the system.

Although factors such as lost reflection of infrared wavelengths fromthe mirror surfaces and poor coupling of fiber to lenses play a role inthese losses, light scattering and other imperfections in the surfacesof mirrors are also significant factors. There is a current need forimprovements in optical switching devices that will reduce the amount oflosses in light outputted by such devices when compared with the amountof light inputted thereto.

Further improvements in optical switching devices, as well as inmicromirror devices in general would be desirable as regards powerconsumption. The utilization of large mirrors relative to the size ofthe light beam can involve rapidly switching high voltages. One avenuefor micromirror device improvement lies in continued miniaturization ofthe devices. In terms of performance, smaller sizes can improve powerefficiency since smaller distances between parts and lower mass partswill improve energy consumption. In terms of manufacturing, continuedminiaturization of mirror elements offers greater yields for a wafer ofa given size.

One other common application of micromirror devices is for adaptiveoptics and phase correction. Although many types of mirror arrayscorrect for tip and tilt such as those discussed for optical switches,often correction of phase distortion is more desired. Even though astatic correcting mirror shape has its uses, phase distortion isgenerally dynamic, and thus the mirror surface must be constantlyupdated. A system such as this generally consists of two parts, whichare a wavefront detector and a deformable mirror. A portion of the lightbeing measured in question is split off and directed to a wavefrontdetector such as a Schack-Hartman sensor which measures tilts of thebeam at various spatial positions within the beam, or a similar sensor.Distortions in the light beam can be detected, and feedback correctionsignals are then sent to a deformable mirror surface to be updated inreal time.

A number of designs for the deformable mirror using MEMS have beenpresented in the last several years. One popular design is that of asingle flexible mirrored surface, with many individual actuators thatdeform the entire surface at each point. Another design is of multiplesmall mirrors, each operating in a manner similar to a piston, with eachindividual mirror actuating perpendicularly to the plane of the mirror.One enhancement to this application can be seen in the presentinvention. Flexible members supporting micromirrors with free ends canallow movement of an entire mirror surface in the vertical direction aswell as allowing for tip and tilt. While the overall range of the devicelimits motion ranges for each of the various types of motion, differenttypes of motion do not interfere with each other, and more than one typeof compensation could be done simultaneously.

Various aspects of the present invention offer improvement in terms ofone or more of the considerations noted above. Of course, certainfeatures may be offered in one variation of the invention, but notanother. In any case, the advances offered by aspects of the presentinvention represent a departure from structural approaches representedby current micromirror designs.

SUMMARY OF THE INVENTION

The present invention involves micromirror structures, optionally usedin adaptive optics or optical switches. Micromirror array devicesaccording to the present invention generally comprise a superstructuredisposed over a substructure including addressing features. Features ofthe superstructure set upon and above the substrate include electrodes,hinges, micromirrors, support members or portions thereof. Supportmembers are provided to hold a mirror/micromirror above the hinge andthe electrode features used to actuate it.

The invention involves supporting each micromirror element above itsrespective hinge portions at or along the sides or corners of themirror. Deformable hinge members are provided for each mirror that arethemselves supported above the substrate by one or more features. Thelocation of supports between the hinge portions and a mirror may vary.Preferred placement locations include opposite corners or sides of themirrors, and alternating (every-other) corner or side locations.Generally, mirrors will have a polygonal plan in which the shapes areclosely-packed (e.g., triangles, hexagons, and quadrilaterals such assquares, rectangles, trapezoids, parallelograms, and rhombi).

In operation, the micromirrors are preferably operated in an analogfashion, although operation in a digital fashion is contemplated. Themicromirrors are supported by hinge structures which allow torsionmotion and flexure or cantilever motion. Individual hinges will mostcommonly have a bent shape with substantially straight section or have acurvilinear profile, either of which facilitates both of these types ofmotions. The structures of the hinges and supports are designed to movein a continuous, controllable fashion simultaneously in at least twoseparate axes. Certain designs also allow for movement of the mirrorperpendicularly to the plane of the mirror in addition to tilt. The bentshape of the hinges which twist as well as move in a cantilever fashiongive enough flexibility of motion to let the mirror tilt and moveperpendicularly at the same time.

By utilizing side-support features according to an aspect of the presentinvention, it is possible to produce certain mirror face embodimentsthat are unbroken by light-scattering or non-reflective features. Thisapproach to mirror and hinge support or attachment described helpsmaximize available reflective surface area. Further details regardingthis approach including other useful design characteristics aredescribed much more extensively in co-pending, commonly ownedapplication Ser. Nos. 10/269,796; 10/269,763 and 10/269,478, each filedOct. 11, 2002 and each of which is incorporated by reference herein inits entirety.

For instance, in connection with such a side-supported mirror approach,manufacturing techniques are taught in which support precursor regionsthat are ultimately removed are temporarily located where space is to beopened upon releasing the individual micromirror elements of an array.As such, the space required for effectively depositing/forming supportstructures is not wasted but falls within space that must be left openanyway in order to allow mirror actuation. In other variations of theinvention, more traditional columnar mirror supports formed within“vias” are provided. However, these are still located near the perimeterof a given mirror.

The present invention includes any of these improvements describedeither individually, or in combination. Systems employing micromirrordevices including the improved superstructure form aspects of theinvention, as does methodology associated with the use and manufactureof apparatus according to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing prior art of a generic torsion barmirror and gimbal assembly.

FIG. 2 shows a top view of prior art showing a single mirror usingflexure hinges as part of an optical switching array.

FIG. 3A shows a perspective view of the present invention in itspreferred embodiment; FIG. 3B shows the same views as FIG. 3A but withthe mirror removed;

FIG. 3C shows the same element from as a side view.

FIG. 4A shows a perspective view of a different configuration of thepresent invention; FIGS. 4B and 4C are similar to those in FIG. 3.

FIGS. 5A-5G show a process for making the device shown in FIG. 3

FIG. 6A is a perspective view of a sample 7×7 array of mirrors shown inFIG. 3 with some of the mirror tops removed; FIG. 6B shows a smallerportion of a similar array of FIG. 4 in its preferred configuration.

FIGS. 7A-7E are perspective views showing a larger array of FIG. 6B usedas a programmable “Fresnel mirror.”

FIG. 8 is a top view of a simple linear 3 by 3 optical switch showingthe mirror elements and light beams.

FIG. 9 is a close up view of a single light path of FIG. 8, includingoptical fiber coupling using a single mirror switching device.

FIG. 10 is a close up view of a single light path of FIG. 8, includingoptical fiber coupling using a multiple mirror switching device.

FIG. 11 is a perspective view of a three-dimensional 4 by 4 opticalswitch showing the mirror elements and light beams.

FIG. 12 is a perspective view of the same switch as shown in FIG. 11,but with two mirrors replaced by multi-mirror arrays.

FIGS. 13A and 13B show prior art for a MEMS-based phase-correctiveadaptive optics technique; FIGS. 13C and 13D show such activity asenabled by the present invention.

FIGS. 14A-14C show the same views of a variant element of FIG. 3 using adifferent flexure design with via electrodes.

FIGS. 15A-15R shows a number of advantageous variants in hinge andelectrode design in simplified form, wherein substantially straighthinge sections are employed; FIGS. 15A′-15R′ shows a number ofcorresponding variants to those in FIGS. 15A-15R in which substantiallycurved hinge sections are employed.

FIGS. 16A-16C show several types of segmented electrode designs withvarying heights.

DEFINITIONS

The phrase “beam steering” refers to operation of one or moremicromirror devices in analog mode by charging address electrode(s) to avoltage corresponding to a desired deflection of the mirror to direct or“steer” the light reflected off the mirror in the intended direction.

The term “diameter,” is defined herein to mean the distance across anylong axis that may be defined. Stated otherwise, the diameter willcorrespond to that of any circle in which the structure can becircumscribed.

The phrase “dim space” or “dead space” refers to areas or spaces in thereflective surface(s) of a micromirror or micromirror assembly which arenot reflective or are poorly reflective.

The term “hinge” refers to a deflectable member or deflectable membersegments together (e.g., as formed by/in a single layer of material);the hinge may be elastically deformed in torsion, bending (tension andcompression), or in some combination thereof.

DETAILED DESCRIPTION OF THE INVENTION

In describing the invention in greater detail than provided in theSummary above, applicable technology is first described. Following thisis a detailed description of exemplary micromirror devices andassemblies according to the present invention, as well as an exemplaryprocess of production. Application of the invention as a programmablelens surface is also discussed. This discussion is followed bydescription of a known optical switching matrix and its function.Finally, the applicability of the micromirrors of the present inventionto optical switch technology, as well as to other fields of adaptiveoptics such as phase-correction is discussed, along with severaladditional variants of the invention.

Before the present invention is described in such detail, however, it isto be understood that this invention is not limited to particularvariations set forth, as such may, of course, vary. Various changes maybe made to the invention described and equivalents may be substitutedwithout departing from the true spirit and scope of the invention. It isalso to be understood that the terminology used herein is for thepurpose of describing particular embodiments only, and is not intendedto be limiting, since the scope of the present invention will be limitedonly by the appended claims.

Methods recited herein may be carried out in any order of the recitedevents which is logically possible, unless the recited language clearlyindicates otherwise. Where a range of values is provided, it isunderstood that each intervening value, to the tenth of the unit of thelower limit unless the context clearly dictates otherwise, between theupper and lower limits of that range is also specifically disclosed.Each smaller range between any stated value or intervening value in astated range and any other stated or intervening value in that statedrange is encompassed within the invention. The upper and lower limits ofthese smaller ranges may independently be included or excluded in therange, and each range where either, neither or both limits are includedin the smaller ranges is also encompassed within the invention, subjectto any specifically excluded limit in the stated range. Where the statedrange includes one or both of the limits, ranges excluding either orboth of those included limits are also included in the invention.

Also, it is contemplated that any optional feature of the inventivevariations described may be set forth and claimed independently, or incombination with any one or more of the features described herein.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although any methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of the present invention, the preferred methodsand materials are now described. All publications mentioned herein areincorporated herein by reference to disclose and describe the methodsand/or materials in connection with which the publications are cited.

It must be noted that as used herein and in the appended claims, thesingular forms “a”, “and”, and “the” include plural referents unless thecontext clearly dictates otherwise. Thus, for example, reference to “amicromirror” includes a plurality of such micromirrors and reference to“the input” includes reference to one or more inputs and equivalentsthereof known to those skilled in the art, and so forth.

All existing subject matter mentioned herein (e.g., publications,patents, patent applications and hardware) is incorporated by referenceherein in its entirety except insofar as the subject matter may conflictwith that of the present invention (in which case what is present hereinshall prevail). The referenced items are provided solely for theirdisclosure prior to the filing date of the present application. Nothingherein is to be construed as an admission that the present invention isnot entitled to antedate such publication by virtue of prior invention.Further, the dates of publication provided may be different from theactual publication dates which may need to be independently confirmed.

Turning now to FIG. 1, a common type of multi-axis mirror is shown insimplified form; this type of design should be well known to those whohave ordinary skill in the art. This is a mirror/gimbal device, andworks by electrostatic attraction of the mirror to four individuallycontrolled electrodes placed underneath the mirror surface. Restoringforce to bring the mirror back to a central position and stabilize it atmany intermediate positions is provided by torsion bars. FIG. 1 shows asingle multi-axis mirror 20, consisting of a mirror surface 22 connectedvia two torsion bars 24 to a frame acting as a gimbal 26 that allowrotation around the Y axis. The frame 26 is in turn connected by twomore torsion bars 28 to a stationary base 30. The frame and mirrorassembly may then rotate around the X axis. Four electrodes 33-36, setin an array 32 can then be charged to various voltages to allow analogcontrol of the position of the mirror in both axes. For instance, ifelectrode 33 is charged to a given voltage while electrodes 34, 35, and36 remain uncharged, the mirror will rotate in both axes toward thatelectrode. By careful control of the voltages of each electrode, nearlyany angle within the range of the device can be set on one particularmirror, as the two axes of motion are able to rotate independently.

This style of micromirror is most often used to direct or steer a singlebeam of light, and is thus relatively large, that is on the order of 1×1mm. Gimbal 26 only moves in one dimension, and the base 30 does not moveat all, which makes these portions of the mirror unsuitable for control.In the figure, the gaps between mirror, gimbal, and base have beenexaggerated for clarity, but still must exist to allow free movement ofthe constituent parts. In an array of mirror assemblies 20, a largepercentage of the total surface of the matrix is unusable.

FIG. 2 shows a different style of known micromirror 38 shown here in asimplified form. In this design, a mirror 40 is attached to a stationarybase (not shown) via four posts 42 by rotationally symmetric flexurebars 44 (in this case, four-fold rotational symmetry). Here the primaryrestoring force is experienced in terms of cantilever-action as opposedto torsion, but the primary axes of movement are the same as the mirrorshown in FIG. 1. The mirror is mounted over an electrode array 32similar to that shown in FIG. 1. Once again, this type of mirror isdesigned to aim a single beam of light, so there is a significant amountof dead space between different mirrors used for the flexure bars andother parts of the stationary frame. Even for aiming discrete beamshowever, it would be advantageous for either of the systems shown inFIG. 1 or 2 for this dead space to be substantially reduced oreliminated. When packed in an array, mirrors such as this can directhundreds of beams at once. With less dead space between mirrors, agreater number of beams could be switched with the same device, as thecontrollable angle for each mirror is limited.

FIG. 3A shows a perspective view of a single micromirror device 46,which will be referred to for purposes of describing techniques formaking the devices according to the present invention. The details ofthe materials employed, intermediate preparation steps and furtherconstructional details associated with the methodology described areknown by those with skill in the art, within the scope of reasonableexperimentation by the same and/or may be appreciated by reference tothe Background section noted above or the following U.S. patents: U.S.Pat. No. 5,083,857 to Hornbeck, entitled “Multi-level Deformable MirrorDevice”; U.S. Pat. No. 5,096,279 to Hornbeck, et al., entitled “SpatialLight Modulator and Method”; U.S. Pat. No. 5,212,582 to Nelson, entitled“Electrostatically Controlled Beam Steering Device and Method”; U.S.Pat. No. 5,535,047 to Hornbeck, entitled “Active Yoke Hidden HingeDigital Micromirror Device”; U.S. Pat. No. 5,583,688 to Hornbeck,entitled “Multi-level Digital Micromirror Device”; U.S. Pat. No.5,600,383 to Hornbeck, entitled “Multi-Level Deformable Mirror Devicewith Torsion Hinges Placed in a layer Different From the Torsion BeamLayer”; U.S. Pat. No. 5,835,256 to Huibers, entitled “Reflective spatialLight Modulator with Encapsulated Micro-Mechanical Element”; U.S. Pat.No. 6,028,689 to Michalicek, et al., entitled “Multi-MotionMicromirror”; U.S. Pat. No. 6,028,690 to Carter, et al., entitled“Reduced Micromirror Mirror Gaps for Improved Contrast Ratio”; U.S. Pat.No. 6,198,180 to Garcia, entitled Micromechanisms with Floating Pivot”;U.S. Pat. No. 6,323,982 to Hornbeck, entitled “Yield Superstructure forDigital Micromirror Device”; U.S. Pat. No. 6,337,760 to Huibers,entitled: “Encapsulated Multi-Directional Light Beam Steering Device”;U.S. Pat. No. 6,348,907 to Wood, entitled “Display Apparatus withDigital Micromirror Device”; U.S. Pat. No. 6,356,378 to Huibers,entitled “Double Substrate Reflective Spatial Light Modulator”; U.S.Pat. No. 6,369,931 to Funk, et al, entitled “Method for Manufacturing aMicromechanical Device”; U.S. Pat. No. 6,388,661 to Richards, entitled“Monochrome and Color Digital Display System and Methods”; U.S. Pat. No.6,396,619 to Huibers, et al., entitled “Deflectable Spatial LightModulator Having Stopping Mechanisms.” In any case, micromirror devicesaccording to the present invention may be produced and/or operatedaccording to the same details or otherwise.

Regarding the features of the present invention, FIG. 3A shows amicromirror device 46 according to the present invention. FIG. 3B showsthe micromirror device 46 minus its mirror 48. FIG. 3C shows the samedevice pictured in FIG. 3B in side view. The mirror surface 48 shown inFIG. 3A is uninterrupted, thereby providing superior reflectioncharacteristics. While the “potential face” of the mirror surface 48(indicated by solid and dashed lines together) may be somewhat largerthan the actual face of the mirror (the area indicated by solid linesalone) reflection losses occurring from “dim” or “dead” space resultingfrom gaps 50 and the spaces between the individual micromirror devices46 in an assembly of devices 46 is more than compensated for by theability to orient the individual devices to direct light that wouldotherwise be lost due to scatter, misalignment, etc., as discussedabove. Further, as described below, the “dim” or “dead” space resultingfrom gaps or openings 50 may be minimized or even eliminated accordingto an aspect of the present invention with careful design of the mirrorsupports 52.

As an alternative to the mirror supports 52 shown, columnar supports orposts (not shown) may be utilized which may be created by filling invias produced in sacrificial material. Supports may have a wall at theedge of mirror (each may have four walls or more or may define curvedsurfaces—depending on the original via shape that is filled-in to createthe structure). Yet, the supports may be inset from the side/corner oredge of a mirror (depending on the style of micromirror device chosen)to which they are closest. However, it may be preferred to position thesupports in such a way as to maximize hinge or torsion member length inview of the mirror style/format selected (i.e., square with cornersupport positions, hexagonal with corner supported positions, hexagonalwith side support positions, etc.). In which case, the base of eachsupport (or an intermediate structure) will be positioned at the end ofany hinge portions. Further details about these support variations canbe found in co-pending, commonly owned application Ser. No. 10/269,796,entitled “Micromirror Systems with Side-Supported Mirrors and ConcealedFlexure Members,” incorporated by reference, in its entirety, above(e.g., see FIG. 9A′ in that application).

However constructed, in the variation of the invention shown in FIGS.3A-3B, the location of the mirror supports are placed equidistant fromone another, forming (in a sense) an equilateral triangle. Accordingly,their location is symmetric along three mirror planes coincident withmirror 48 (i.e., they offer three-way symmetry). Another way of lookingat the arrangement is that the supports are present on alternatingcorners. As such, opposites of the mirror have no support counterpart(supports are inopposite one another).

In certain other variations of the invention pictured (e.g., in FIGS.4A-4B), each of a pair of supports is actually positioned opposite oneanother and across the body of mirror 48. Advantageously, the supportpositioning produces bilateral symmetry. Equidistant placement about themirror face is again preferred. In any case, equal spacing or providingsome measure of symmetry offers greater predictability in control forvarious modes of mirror actuation (i.e., it produces substantiallyequivalent behavior). For the same reasons(s) a measure of rotationalsymmetry in hinge structure is often desired—as is apparent in thefigures embracing aspects of the present invention.

Moving on with further details of the invention, one such aspectconcerns the manner in which mirror 48 is attached to its hinge.Supports 52 on several sides of mirror element 48 secure it to hingeportions 54 of an overall hinge 57. Hinge portions 58 are attached tosubstrate 60 by a central hinge joint 63 that underlies a portion (thecenter, in the example shown in FIG. 3B) of the mirror element 48. Eachhinge 57 (formed by portions 54, 55 and 58) is provided in a singlepiece of metal, constrained in the center to act as three separateflexure pieces or deformable member portions. A base 72 of each support52 may directly connect each hinge portion 54. Alternatively, anintermediate layer or nub 74 of material (e.g., serving as a bondinginterface) may be employed. In any case, the hinge elements are hiddenor concealed beneath the mirror.

Hinges 57 are elevated above substrate 60 to permit torsion andcantilevered flexure about portions 54 and/or 58 as the mirror element48 is tilted or rotated about various axes. The two portions 54 and 58of each hinge are connected at a bend 55 that allows greater movementand flexibility. Although other types of central support are possible,hinge joint 63 is a via-type support structure, preferably openunderneath the hinge center 67, except for a central post 69. Thedistance the hinges are set above the surface of substrate 60 may be aslittle as about 0.1 micron, or less.

As to the separation between the hinge portions and the underside ofmirror 48, this may—likewise—be as little as about 0.1 micron, or less.Hence, the mirror of each micromirror device or element to be providedin an array or otherwise may be located as little as about 0.2 micron,or less, above the surface of substrate 60.

Avoidance of a central yoke to hold the mirror structure (as in knowndevices produced by Texas Instruments) allows creation of very lowprofile micromirror devices by the invention that are still able toattain high deflection angles (typically about +/−10 deg., even upwardsof about +/−15 deg., to about +/−20 deg. or more). Of course,mirror/micromirror devices according to the present invention may beadvantageously manufactured on a larger scale (even using MEMStechniques)—possibly utilizing other actuation techniques, includingelectromagnetic, electrostatic, thermo-mechanical or piezo-basedapproaches.

An aspect of the invention that facilitates provision of adequateelectrostatic attraction in response to hinge restoring forces thatincrease with angular deflection has to do with the configuration ofelectrodes 76. The electrodes may be configured with a plurality ofportions 78 and 80 (or more) at different levels. Whether provided in aseries of steps by continuous or contiguous members (as shown with asupport portion 82 between each stage 78/80), by steps formed withdiscrete members or a continuous angled member, the electrodes areconfigured so that portions further from the center or point of rotationof the mirror are at a lower level. In this configuration, all threeelectrodes 76 are of identical shape. Similar electrode shape and areasimplify the process of actuating a multi-axis mirror system, but otherconfigurations of electrode shapes and sizes, including asymmetricvariants are possible. In this case, there is a plurality of baseportions 80 for each electrode for added structural stability, althougha singular base portion 80 may be preferred.

The electrode configuration shown with higher portions closer to thecenter of the mirror or overall device and lower portions more distanttherefrom provides clearance for the mirror as it is tilted at an angle.Furthermore, the configuration provides for sequential attraction ofmirror 48. When the mirror is angled away from a set of electrodes, theupper electrode portion is the first to exert significant attractiveelectrostatic force on the mirror (in light of the inverse squaredrelationship between electrostatic attraction and distance betweenobjects). As the upper electrode portion(s) effectively attract themirror drawing downward (i.e., towards the upper electrode portion), theinfluence of the electrode lower portion(s) increases as the distancebetween the lower portion(s) and the mirror decreases. Further aidingattraction of the mirror to its full angular displacement is theincreased mechanical advantage or lever arm offered at more remoteregions of the mirror interacting with lower electrode portion 80. Thisand other variants of possible electrode shapes are explored more fullyin application Ser. No. 10/269,763, entitled “Micromirror Systems withElectrodes Configured for Sequential Mirror Attraction,” which isincorporated by reference herein in its entirety.

Device 46 is actuatable to move in a plurality of axes. One differenceof the present invention is one of scale. Advantageously, the scale ofthe present invention may be made much smaller than currently availablemicromirrors, with the diameter of each mirror element being on theorder of magnitude of 10-20 microns, or more. An array of hundreds orthousands of these micromirrors may be used to replace a single mirrorelement as shown in FIGS. 1 and 2. A greater number of micromirrors foreach portion of the incoming wavefront provides for much morecustomization of the properties of the outgoing wavefront. Miniaturizingthe individual mirror size carries a number of other benefits that willbe detailed later. Nevertheless, it is contemplated that the size of themirror diameter may be increased to as high as about 1 mm or more, withdimensions of the other components of the device having increaseddimensions in proportion thereto. This would allow a single mirrorelement of the present invention to effectively control an entire lightbeam.

In the configuration shown in FIG. 3, the hinges are supported on thesubstrate at the center of the device. FIG. 4 shows another highlyadvantageous design, but with the hinges being supported on the outsideof the device. The features of this mirror assembly 47 are displayedsimilarly to that of FIG. 3. Many of the same features are present, butare connected in a different fashion. In this variation, the base andmirror are square, although a hexagonal or other shape would also workwith this type of hinge structure.

As in FIG. 3, FIG. 4 shows a mirror 48 connected to a hinge portion 54.The other end 58 of each hinge portion 57 is connected to a hinge joint62. Similar to FIG. 3, the hinge portions 54 and 58 are connected by abent portion 55. As compared to device 46 in FIG. 3, in device 47,hinges 57 are physically separated.

Hinge joints 62 are bridge-type support structures, preferably openunderneath the hinge center 64, which is attached to a spanning segment66 between vertical support segments 68. Feet 70 may additionally beprovided to stabilize the support structure. Yet another option is toproduce support segments 68 at an angle relative to the surface of thesubstrate (i.e., having both vertical and horizontal components).Features of the electrodes 76 are essentially equivalent to those aspresented in FIG. 3.

Each of the designs presented in FIGS. 3 and 4 are connecteddifferently, but they both offer much of the same function. Both aredesigned to tilt in a plurality of axes simultaneously in a mannersimilar to that shown in U.S. patent application Ser. No. AttorneyDocket No. EXAJ-003, entitled, “Multi-tilt Micromirror Systems withConcealed Hinge Structures,” filed on even date herewith andincorporated by reference. Yet, because the hinges have been designed toallow both torsion and cantilever, they are also flexible enough toeasily permit movement of the mirror in the direction perpendicular tothat of the plane of the mirror surface. By providing for multi-axistilt and vertical motion (relative to the substrate) the devicesaccording to the present invention allow for correction of both tilt andphase as discussed below.

Further differences between the center-supported and end-supported hingestructures in aspects of the invention (e.g., as in FIG. 3 vs. FIG. 4)concern deflection angels as may be obtained for each givenconfiguration. Namely, use of a central support clear regions otherwiseoccupied by hinge supporting structure. Accordingly, greater deflectionangels can be achieved for central-supported devices than end-supporteddevices of the same thickness (mirror height).

The manner in which a micromirror device 46 according to the presentinvention may be produced is illustrated in FIGS. 5A-G. Of course, theprocess steps employed will vary depending on which inventive featuresare actually employed in a given variation of the invention, as would bereadily apparent to those of ordinary skill in the art.

In FIG. 5A, a sacrificial layer of material 84 is set upon substrate 60.It is patterned with a first mask 86 to define a substrate-level portion88 upon etching. In FIG. 5B, a hinge metal layer 90 is deposited overthe entire surface including a portion of the sacrificial layer. Asecond mask 92 is utilized in defining a passivation layer (not shown)over the region(s) of layer 90 serving as a hinge precursor region 94.Metal layer 90 fills in vias 96 provided in substrate 60 to form aconnection 98 between underlying address circuitry beneath an oxidelayer of the substrate. The same approach to addressing and substrateconstruction may be employed as described above, or another manner ofelectrical control of device superstructure produced may be utilized.This holds true with respect to connectivity between the device elementsas well as the configuration of substrate 60.

As shown in FIG. 5C, a thicker layer of conductive material 100 isdeposited over the hinge material. This layer builds-up the electrodes76 and nubs 74, and hinge support 63 for hinge portions 57. Layer 100also further fills in via 96 and connecting structure 98. A third mask102 is employed to define a protective layer (not shown) over the regionof layer 100 serving as electrode precursor(s) 104, nub precursors 106,and hinge support precursor 108.

In FIG. 5D, layers 90 and 100 are shown selectively etched to revealhinges 57, hinge joint 63, and electrode portions 76. In FIG. 5E, onecan see another sacrificial layer 110 which then covers thesestructures. A fourth mask 112 is used to pattern sacrificial layer 110to form mirror support precursor regions 114 upon etching thesacrificial layer.

FIG. 5F shows sacrificial layer 110 as it is selectively etched, andthen coated with a layer 116 of conductive material suitable to serve asa mirror (or a substrate that may be subsequently coated with a highlyreflective metal or dielectric material). A fifth mask 118 is used inorder to define a passivation layer over mirror precursor regions 120 tobe retained, but not the adjacent borders 122, which are removed to formspaces between adjacent micromirrors 46.

FIG. 5G shows a micromirror element 46 according to aspects of theinvention after all sacrificial materials have been removed. Asdiscussed above, the mirror is supported at or along its opposite sidesor edges by supports attached to a hinge, which is in turn supportedabove the device substrate. In addition to being placed at varioussides/portions of the mirror, the support members may be characterizedas being “open” in nature. Progressive or dual-stage electrodes areshown as well.

FIG. 6A shows an exemplary array assembly 124 of micromirrors 46 in aseven across arrangement. Part of the tops of the surface of the mirrors48 have been removed to show the underlying structures. This type ofmirror array, comprised of potentially millions of individuallycontrolled mirrors, can be used for a number of applications. Not onlycan the micromirrors 46 of assembly 124 be positioned to mimic a tiltingof micromirror device 20 about its tilt axes (or some combination ofboth) and thus represent a flat reflective surface, but the micromirrors46 can be independently positioned to form a “smart surface” (i.e., onethat can be adapted to modify the shape of a reflected wavefront, inresponse to a given wavefront that is made incident thereon). For thisreason, assembly 124 can be described as a “Fresnel mirror” or a“programmable lens”. FIG. 6A can also be seen or regarded as only asmall section of a much larger array having a million such mirrors ormore. Of course, array size will vary upon choice of application and thenumber of mirrors reference is in no way intended to be limiting.

Array 124 as shown in FIG. 6A has some advantages because of itssimplicity in layout. Additionally, addressing for this layout would beconsistent for each mirror element 46. A similar array of mirrors can bemade from device 47 shown in FIG. 4, with each mirror element being setin the same orientation in a square array.

However, it may be preferred to use a different layout of mirrorelements 47 as shown in FIG. 6B. Here, a smaller 2 by 2 section of aslightly different array 126 is displayed. In this configuration, thedevices 47 (shown without their mirror top as in FIG. 4B) are unchanged,but the orientation of the elements 47 varies. Every other mirrorelement 47 is rotated by 90° in a checkerboard pattern. The mainadvantage is seen in the position of the hinge supports 62, for whicheach support 62 meets at a corner with three other supports 62 to makeone large support 128 common to the adjacent deformable hinge portions.Large support 128 reduces the number of discrete features to bemanufactured, and offer greater structurally stability than individuallymanufactured supports 62. In addition, because the structure shown inFIG. 6B is a combined structure (as opposed to four free standingelements), the overall dimensions of the support can be made smaller,which can lead to longer hinges and more mobility of the hinge.

Micromirror arrays 124 or 126 provide great versatility in their abilityto form surfaces for performing wavefront correction/shaping, and bytheir ability to be oriented to form other than flat surfaces, includingconfigurations which form effective programmable lenses. Examples ofsuch configurations are shown schematically in FIG. 7A-E. FIG. 7Adisplays an array similar to the same array assembly 126 as seen in FIG.6B. For illustrative purposes, a lowercase “e” 130 is used as a sampleobject to be reflected off mirror assembly 126. The image 132 resultsfrom the particular configuration of the micromirrors. A dotted line 134portrays where the “e” is reflected on the mirror surface, and the pathof light follows an arrow 136. In FIG. 7A, the array is set completelyflat, so there is little change in the image other than simplereflection. For comparison to later figures, the image 132 is setagainst a reference set of crosshairs 138.

For simplicity, FIGS. 7B-E will all use the same object 130 as seen inFIG. 7A, which will be omitted in these figures. Only the final image132 will be shown. FIG. 7B shows mirror array 140, which is the samearray as 126, but with all of the mirrors tilted in the same direction.The image 142 size is unchanged, but its position has moved. Thus thearray 140 acts here as a tilting flat mirror. FIG. 7C displays an array144, once again the same array 126, but this time individual elements 47are tilted to approximate the surface of a focusing mirror, as can beseen in the resulting image 146, shown having a reduced size.

FIG. 7D shows a similar array 148 that is now set with mirror elements47 approximating a defocusing mirror, which again can been seen in acorrespondingly larger image 150. In FIG. 7E, array 152 displays bothtilt and focus on the same set of mirrors, with the results showing upin image 154. Because each mirror element can be set independently ofeach other, potentially several types of correction could be implementedsimultaneously. Although tilt and focus can be addressed on the same setof mirrors, there are some important limitations. Depending on thedimensions of the components, tilt angles of individual mirrors might beonly as much as 10° in each axis. However, tilt angles of some designsmay be as large as 20° or more. If a set of mirrors is tilted acting asa flat mirror so that all of the mirrors are near or at their maximumangle, it will not be able to further focus or defocus the bean. Inaddition, tilting of curved surfaces can lead to astigmatism in thereflected beam, although this can be corrected by careful shaping of theprogrammable lens at the specified angle.

Although they are not shown here, many other types of wavefront shapingare possible. Various types of lenses other than spherical can becreated, such as cylindrical or parabolic mirrors. Distortions in theincoming beam due to imperfections in earlier surfaces can be detectedand corrected. Any number of other surfaces can be created subject tothe angular limitations of the micromirrors.

In practical use, such a small subset 126 (or 124) of a much largermirror array would not be used for shaping beams or images, but thissize is used here for illustrative purposes. The mirrors in a somewhatlarger portion of the array shaped in this manner would not be seen asclearly to have a curvature because the differences from one mirror tothe next would be slight. One advantage to the independently addressablenature of these mirrors is that the array as a whole can be divided intomany fields, each with their own properties. One simple way toaccomplish this is to use a defined grid, where the center of eachsubsection of the grid is set to be the center of a programmable Fresnelmirror, each with its own focal length and tilt angle. The presentinvention is not limited to this manner of controlling the micromirrors.Any arbitrary number or shape of field may be independently controlled.

Another important application of the present invention is in the area ofswitches for optical networking. Looking at FIG. 8, a schematicrepresentation of a switching matrix 154 is shown. For simplicity ofexplanation and drawing, only a linear matrix 154 is shown, althoughtwo-dimensional matrices are also commonly used. The matrix of FIG. 8includes two arrays 156, 166 of steerable micromirrors (158, 160, 162and 168, 170, 172, respectively). Each of the micromirrors are“steerable” by their operation in analog mode, which involve actuationof micromirrors 158, 160, 162, 168, 170, 172 to a voltage correspondingto a desired deflection of the mirror surface of the micromirror, as isknown to those of ordinary skill in the art.

In this way, each of the three micromirrors 158, 160, 162 can be tiltedabout an axis of rotation so as to direct an optical signal receivedfrom its input channel (163, 164, 165 respectively) toward any one ofmicromirrors 168, 170, 172 that corresponds to the output channel 173,174, 175 that is desired to be outputted to. Input and output channelsare often optical fibers with focusing optics. For example, micromirror158 can be oriented to reflect an input signal received from inputchannel 163 to micromirror 168, which, in such instance, is also tiltedto optically couple the output from micromirror 158 with optical outputfiber 173. Alternatively, the voltage can be varied to the electrode(s)of micromirrors 158 and 172 so that they are optically coupled with oneanother in which case the optical input from optical input fiber 163 isoutputted to optical output fiber 175, and so forth. U.S. Pat. No.6,389,190 describes a switching matrix of the type shown in FIG. 8 indetail, including an example of MEMS micromirrors that may be employedin the construction of such a switching matrix.

As noted in the Background section of the present application, currentlyavailable optical switching mechanisms experience a significant loss ofthe optical signals passing from an input to the output thereof, i.e. onthe order of a 60% to 70% loss. Significant contributions to theselosses are due to scatter of light from the light signal as it passesfrom an input optical fiber to first and second mirrors (in input andoutput mirror arrays) and finally to an optical output fiber.Aberrations in the surfaces of the micromirrors on the input and outputarrays can contribute to the scattering of light as well as todeformation of the light beam to the extent that a portion of the lightbeam can become misaligned with the output optical fiber by the timethat the input optical signal (light beam) has been reflected off aninput side micromirror and an output side micromirror. Misalignment ofthe fibers to the mirrors can be a significant source of loss, inaddition to loss coupling into the output fiber due to mismatched beamsizes.

Another source of error can be created if the tilt axes of the input andoutput mirrors are not parallel in an arrangement such as shown in FIG.8, although this primarily affects only arrays of mirrors that only havea single axis of movement. In such a case, opposing input and outputmirror surfaces of input and output side micromirrors, which areintended to be aligned to optically couple an input optical fiber and anoutput optical fiber, can never be aligned in parallel, which results ina skewing of the optical beam such that a portion of the output signaldoes not enter the output optical fiber. Similar negative effects canoccur due to thermal and other environmental effects, as well as agingof the components.

The present invention can be applied to optical switching configurationsto correct for, and thereby substantially eliminate sources of lossesdue to misalignment of mirrors, imperfections in mirror surfaces andother physical causes of light loss through a switching mechanism. FIG.9 is a schematic, two-dimensional representation of a switchingarrangement which shows only one micromirror device (158, 168respectively) from each of the input and output arrays, for simplicityof discussion. An optical input signal is incident upon micromirrordevice 158 as delivered by input channel 163. Seven light rays 177-183representing parts of a single light beam are schematically representedin FIG. 9 as being incident on the mirror surface of micromirror device158, from which they are then reflected toward micromirror device 168and are then directed to output channel 173, where 158 a and 168 arepresent the axis of rotation of these mirrors. In this example, lightrays 177 and 183 become misaligned with the mirror surface ofmicromirror device 168 due to expansion of the beam hitting the mirrors.Similarly, light ray 179 is misdirected and is not delivered to outputchannel, due to light scattering which may be caused by a lack offlatness in the mirror surface of micromirror device 158 or othermalformation which cause misalignment of the light reflecting off of aportion of the mirror.

Note that although the micromirror devices 158 and 168 are adjustable bytilting about axes 158 a, 168 a, that any further adjustment of themicromirror devices 158, 168 in FIG. 9 would not result in a reductionof light loss. For example, if micromirror 158 were tilted by a slightrotation in the clockwise direction, then ray 183 might be directed ontothe surface of micromirror 168, but at the same time, ray 178 might thenmiss the reflective surface of micromirror 168, and certainly ray 177would still not be reflected off of micromirror 168. Similarly, whilerotation of micromirror 168 in the counter clockwise direction mightdirect ray 177 into the optical output channel 173, it would alsomisdirect ray 178 at the same time, so as to no longer be channeled intothe output channel 173.

By replacing each of the micromirror devices 158, 168 with a pluralityof smaller and more controllable micromirror devices 46 as shown in FIG.10 according to the present invention, a micromirror assembly (184, 186,respectively) is provided to replace each of the micromirror devices158, 168 of FIG. 9. Each micromirror assembly is made up of a plurality(seven, in the non-limiting schematic example shown) of micromirrordevices 46 (labeled here as 46-1 through 46-14), each of which isindependently controllable for movement of a mirror surface about twoaxes of rotation independently, or about an unlimited number of axes ofrotation defined by the resultant vectors occurring when rotating tovarying degrees about both axes of rotation. In the example shown, themicromirror device 46-1 has been rotated or tilted in the clockwisedirection so as to align ray 177 with the corresponding micromirror(46-8) on assembly 186, so that ray 177 is now properly channeled to theoptical output channel 173. It is noted that the rotation of micromirror46-1 is shown in an exaggerated fashion for purposes of explanation, andthat the actual rotation of the mirror would be much less, so as to beessentially imperceptible, while having the effect of “flattening” thereflective surface in this location for reflecting the ray 177 in thecorrect direction. Similarly, micromirror 46-7 is tilted or rotatedsomewhat counterclockwise, so as to accurately direct light ray 183 tobe incident upon micromirror device 46-14, which in turn directs the ray183 into the optical output channel 173. The micromirror device 46-3 inassembly 184 has been tilted or rotated in the counterclockwisedirection to redirect ray 179 into the proper position on assembly 186to permit proper direction into the output channel.

In this particular example seen in FIGS. 9 and 10, the light beam fromoptical input channel 163 is shown slightly expanding to illustratedetails of the present invention. In an actual system, the light beamwould be carefully focused to keep the spatial profile of the beam assmall as possible throughout the length of the optical switch. Bykeeping the beam size small, the size of the individual mirrors and thespacing between them can be made smaller as well, which allows for ahigh density switching matrix. This is desirable, since MEMS micromirrordesigns generally have a limited usable angular range of movement, so agreater density leads directly to a higher port count in the switch.Changing the beam size in this manner has several adverse consequenceshowever. Even if all of the rays are focused so that they hit thefocusing lens at the output channel, the outgoing angle of each ray(177-183) may not be best for good coupling efficiency into the fiber.Adjustment of both of the switching mirrors for best coupling does noteliminate much of the loss. To accommodate for relatively large spacingbetween the mirrors, often a long distance between mirrors is needed.Maintaining small beam spot sizes throughout a longer distance requiresvery good uniformity of focusing elements on the incoming beams. Theseconstraints can make it difficult to create a working device with a highport count when using larger flat mirrors.

By providing a plurality of independently adjustable micromirrors 46 toform each micromirror assembly (such as 184 and 186), input and outputarrays of these assemblies can then be constructed in making an opticalswitching or cross-connect apparatus which is capable of reducing theamount of light loss, as compared with those currently available. Theability to independently adjust devices 46, in effect, gives theassemblies the ability to optically adapt to the wavefront of theoptical signal that is being received, and to manipulate that wavefrontto maximize the amount of the signal that is ultimately received at theoutput end of the switching device. The reflective surfaces of themicromirrors 46 in assemblies 184 and 186, as has been previouslymentioned, can thus be used as programmable Fresnel mirrors to focus thelight received and reflected so as to minimize losses. It is much easierto keep light focused properly over a short distance as opposed to along distance. Using a plurality of mirrors allows any focusing elementafter an input fiber to be optimized for only a short distance to thefirst mirror array. The first mirror array can focus properly to thesecond mirror array, and the second mirror array will then focusproperly for good coupling into the output fiber.

Although a small amount of light is lost due to the spacing between themicromirror devices 46 in each array, this loss is small compared to theamount of light that would ordinarily lost by a system such as shown inFIG. 9, but which is recaptured by proper orientation of themicromirrors 46 as discussed with regard to FIG. 10. Although theexample of FIG. 10 has been described with regard to a one dimensionalassembly of micromirrors 46 to form the assemblies 184, 186 (i.e., a 1×7array of the micromirrors 46 in each assembly), it is to be noted thatthe present invention is in no way limited to such arrangement, as sucharrangement has been described only for purposes of simplicity. In fact,the more likely assembly is to include a two-dimensional array ofmicromirrors 46 to form each assembly, even with a switching setup asshown in FIG. 8. For example, a micromirror device 20 can be replaced bya 10×10 or 100×100 array of micromirrors 46 to form an assembly such asthe array 124 shown in FIG. 6. Because the micromirrors 46 have theability to tilt or rotate about two axes (or combinations thereof, asnoted above) it is preferable to form a two-dimensional array of themicromirrors in each assembly, for three-dimensional redirecting, orfocusing, of incident light signals.

FIG. 11 is a schematic representation of a three-dimensionalcross-connect arrangement 190. In this arrangement, the micromirrordevices can be three-dimensionally positioned so as to optically connectany micromirror in the optical input array 192 with any micromirror inthe optical output array 198. Thus, for example, by appropriate positionof micromirror 194 and a corresponding micromirror in the optical outputarray 198, the optical input 204 can be directed to be outputted to anyof optical outputs 206-209 by appropriate optical connection ofmicromirror 194 with respective ones of optical output micromirrors200-203. Each of input side micromirrors 195-197 has similarpossibilities, with the appropriate corresponding adjustment of theoutput micromirrors.

FIG. 12 is a three-dimensional cross-connect 210 similar to thecross-connect 190 in FIG. 11, but with two of the mirror elements 194and 196 being replaced by exemplary 5×5 arrays 214 and 216. Replacingthe single mirror elements has a number of advantages already addressed,but which may be more apparent as seen in this figure. In this example,the two arrays are set to act as two different focusing elements for thebeams being switched. If input beam 204 has slightly changed focusingcharacteristics than input beam 218, the array elements can be adjustedindependently to maximize the coupling efficiency. Most often, the inputbeams of an optical switch are focused coming out of an optical fiber byeither a lens array or an individual lens on each fiber. Uniformity offocal lengths for these lenses can be very difficult to achieve, yetsmall changes in the consistency of these lenses can have a large effecton the focusing of the beam, and thus on the efficiency of couplinglight back into the output fiber. Using a small array of mirrors to actas an additional lens element as a part of the optical path allows forslight changes in the input beam without sacrificing power throughputinto the output. In an actual system based on these designs, all of therest of the input and output mirrors 195, 197, 200-203 would berepresented by a similar array of micromirrors.

Another advantage of the multimirror array is that of positioning. In asingle mirror system as shown in FIG. 11, each input fiber must beprecisely aligned to the center of its corresponding mirror along withall the other input fibers. Small irregularities may make the input beamclip on the edge of the mirror or miss it altogether. Individualadjustments of each fiber and/or focusing components is commonly notpossible, so much of the time, the entire array of input fibers andlenses are aimed to find the best compromise position, even thoughthroughput on many of the channels suffers as a result. Achieving exactuniformity is no simple task. One possible solution for this problem isto make the size of each individual mirror in the arrays 192 and 198larger. While this reduces the problem of losing power from the beam atthe edges of each mirror, it does have the drawback of lowering thedensity of the mirror array as a whole, which as has already beendiscussed, will lower the total port count of the switch. In FIG. 12, asingle mirror is replaced by an array of mirrors. In actuality, eachsingle mirror would be replaced by an array of mirrors with noparticular boundaries between the original surfaces of the singlemicromirrors, but which was displayed in this fashion for clarity. InFIG. 12, between array 214 and 216 would appear a number of identicalmirrors; in aggregate, all of the mirrors would make a single largearray. If the center of a single fiber was tilted incorrectly by a smallamount to change the position of its input beam on the mirror array,this new location could be chosen as the center of its steering set ofmirrors with no extra loss to the beam falling off an edge. Of course,uniformity of the input fibers and beams cannot be so poor as to overlapparts of more than one beam at any one place on the array as a whole,but small changes that would adversely affect performance onsingle-mirror systems will not harm throughput here. In addition, thelack of boundaries for the array domain of a single light beam allows atighter spacing of the beams, which as has been mentioned previously,would allow for a higher density switch with greater port count.

FIG. 6A showed an assembly of micromirror devices 46 that comprise thepresent invention which form a micromirror assembly 124 effective toreplace micromirror device 194 (or any of the other micromirror devices195-197 and 200-203) in FIG. 11, although this size of array is notlimiting. A typical micromirror device currently used in the opticalswitching field employs a mirror surface having width and lengthdimensions of about 1 mm×1 mm. Using present techniques, micromirrordevices 46 or 47 according to the present invention may be made to havea mirror surface as small as about 8 microns by 8 microns. Thus, anassembly of 15,000 micromirrors (i.e., a 125×125 array) could beprovided to replace a single micromirror device in the prior art. Asnoted previously, the present invention is not limited to this size ofmicromirror, as micromirrors having dimensions larger than 8 microns by8 microns can certainly be made, such that an assembly having aplurality, but a lesser number than one hundred micromirror devices 46could be assembled to replace a single known micromirror device. Also,it is contemplated that even smaller micromirror devices 46 will bepossible as the state of the manufacturing arts progresses.

Another important application of the mirror devices in the presentinvention is one commonly used in adaptive optics, which is that ofphase-correction. This has been increasingly utilized in various fieldssuch as astronomy or confocal microscopy to improve the quality of theirimaging techniques, in some cases drastically. The primary component ofa phase-correcting adaptive optics system is a deformable mirrorsurface, which was discussed in general in the Background section butwill be shown here in more detail. The deformable surface is generallychanged in real time to correct for phase distortions between variousportions of the image.

FIG. 13A shows a portion of a common type of adaptive optics mirror usedin the prior art in a simplified form. The mirror assembly 240 iscomposed of a single flexible mirror surface 242 over a substrate 246.The mirror surface 242 is held over the substrate 246 by a sparse arrayof linear actuator elements 244, six of which are shown here. Actuatorelements 244 might work using a variety of methods, such aselectrostatic attraction, piezoelectric effects, thermomechanical, orothers. Spacing of actuators 244 is normally chosen to maximize controlof the mirror surface but minimize complexity. Because the mirrorsurface connects all of the actuators into one large system, moving themirror to a desired shape can involve complicated interactions betweenvarious elements 244. Often detailed models are needed in order toadjust the mirror surface 242 to a desired shape. One advantage to thistype of system is that the reflective surface is single and unbroken.

FIG. 13B displays a similar device 248, but in this case, individualmirrors 250 replace the large mirror surface 242. As can be seen here,the heights of the mirrors can be adjusted to mimic most any shapecapable of by device 240. In comparison, this mirror surface has anumber of small gaps in it, which may scatter incoming light, especiallyif the gaps are too large. This is compensated for by the flexibility ofthe device and the straightforward control, as each mirror's positiondoes not affect the one next to it. For ease of comparison, the twodevices shown in FIGS. 13A and 13B are the same scale, although this isnot typically the case. In most cases, the multimirror device 248requires many more micromirrors and a higher density of actuators toachieve the same shape; power consumption of this device can be higher.

A device that can be built with the present invention bears someresemblance to array 248 in FIG. 13B. FIG. 13C shows an array ofindividual elements 46 that can be actuated in an up/down fashion. Ifall of the electrodes of a particular mirror element such as 46 aredriven at the same voltage, equal force will be applied to the entiremirror in the vertical direction perpendicular to the plane of themirror. Because the design of the hinges gives great flexibility, theassembly 46 should have dynamic range down to the stopping point of themirror. However, as shown in FIG. 13D, with mirror elements according tothe present invention, additional features may be offered. Namely, oneof the advantages of the inventor's designs is the ability to actuatemirrors in multiple axes at once. Unequal driving voltages on thevarious electrodes will both tilt the mirror and drive it verticallysimultaneously.

Thus, both tilt-correction and/or phase-correction of incident light canbe implemented on the same surface. This not only can greatly simplifythe control electronics needed to drive the system as a whole, but alsomay have other optical benefits as well. In some types of systems,spatial distortions can be created in a light beam when the tip/tilt andphase-corrective surfaces are separated in space. By having bothcorrections performed by the same surface, some artifacts such asparallax errors can be eliminated

Note also that scale of the micromirrors can play an important rolehere. In the micromirrors 46 as described earlier, the preferred size ofeach mirror is relatively small, down to the order of 8-10 microns indiameter. Smaller sizes allow for lower power consumption and greaterangle for a given mirror height. This may not be best forphase-correction applications; many of these applications need movementof the mirror surface to be several wavelengths of the light inquestion. In most cases, this is no more than several microns. Thesmallest scale of the mirrors does not allow for this range of movement.Creating the micromirrors somewhat larger or with different thicknessesof components will allow for a greater range, but may limit the anglepermitted for tilting. It is likely that for a mirror surface thatallows both tilt and vertical movement, the scale chosen will have to bea compromise between these two extremes to give a device useable forboth types of movement, at least for some applications. For otherapplications, little transverse movement of the mirror is necessary, andeven the smallest mirrors will work well.

A number of other variants to the design of the present invention arepossible other than the one shown in FIG. 3. FIGS. 14A-C provide detailsof a micromirror 220 with a hexagonal-shaped mirror top supported atseveral side positions. Its construction and appearance closely resemblethe micromirror elements 46 shown in FIGS. 3A-C, and views for each partof the figure are the same. In this variant of the device, thehexagonally shaped mirror 48 is attached to the hinge structure 54 atits side supports 52, another hinge portion 58 is attached to thesubstrate 60 with a similar hinge joint 63.

As for hinge structure, a difference to be observed is that each hingestructure 57 includes an additional bar/section 61 between the other twoportions of the hinge (54 and 58). Longer hinge sections as thusprovided offer more compliance than that of hinge 57 in FIG. 3, and mayallow for easier actuation of the mirror. A potential drawback in thisdesign, however, is that the additional area taken up by the largerhinge impinges on area previously taken up by electrode 76. Yet, thegreater movement allowed by the longer hinge structure should make upfor this deficiency. As noted above, the selection of certain featuresof the invention for their relative benefits may depend on theapplication sought.

Another difference in this design as compared to that in FIGS. 3A-3B isshown in the electrode design. In FIGS. 14A-114C, instead of a staggeredmulti-level electrode 76, a single stepped electrode 226 is shown. Usinga via-based support column 228, the entire electrode surface 230 israised close to the mirror. This configuration allows for the maximumelectrostatic attraction.

Although a via electrode may be preferred in that less voltage should beneeded to achieve the same degree of electrostatic attraction, formanufacturability, a staggered electrode may be preferred. A via-typeelectrode may potentially block the mirror from reaching its maximumangle of tilt in certain directions for some electrode/hinge layouts.One other electrode variant, not pictured here, is that of using a flatsingle electrode low on the substrate 60. Although this design wouldhave the least electrostatic attraction, and thus be more difficult toactuate, it would be very simple to manufacture. Of course, any of theelectrode designs described with regard to the example in FIG. 14B isnot limited to the micromirror shown in FIG. 14, but may be applied toany of the other designs described herein and vice versa.

Note that regardless of the choice of electrode configuration in any ofthe invention's variants, the hinges, mirror, and electrode have beendesigned not to interfere with each other. Because the hinge andelectrode layers are constructed at the same time, there is no overlapbetween them except at the junctions. At the mirror's maximum angularextension in both axes, the mirror touches down only on the substrate 60or on the hinge supports 62. While in normal operation, the mirror andattached metal structure are charged up to a bias voltage, and theaddressing electrodes are charged to a different voltage, there is nodanger that the structures will short out and potentially damage ordisable one or many other mirrors.

A number of other configurations of hinges and electrodes are possibleusing the same conceptual framework than have been taught here. Aschematic view of some of the connectivity possible is shown in FIG. 15.The schematic mirror layout 252 in the upper left hand corner of FIG.15A corresponds to the design presented in FIGS. 3A-3C; that of FIG. 15N corresponds to the design of FIGS. 4A-4C is in; FIG. 15C correspondsto FIGS. 14A-14C.

In each mirror layout, a dark circle 256 corresponds to a generalizedconnection to the substrate, dark lines 254 correspond to hingematerial, and open circles 258 correspond to connections of hingematerial to the mirror. The listing of possible configurations in eachof FIG. 15 is by no means intended to be exhaustive, and is only asample of the possibilities covered herein. In addition, although forsimplicity only hexagonal and square shapes are shown, many other shapesare possible that neatly tile a plane. The designs shown, however may bemost preferred for the superior capabilities they offer as determined bythe present inventor.

Still further, it is noted that the variations of the inventionschematically pictured in FIGS. 15A-15R are represented by counterpartsin FIGS. 15A′-15R′. These “counterparts” that employ substantiallycurved hinge sections. In both sets of figures, the hinges share thecommon characteristic of having components or portions that are directedalong different paths (i.e., that extend in different directions). Forstress relief purposes, it may in fact be the case thathinges/deformable members with a more or less curvilinear profile areemployed in the invention.

Still further variation possible in connection with the presentinvention has to do with multiple electrodes replacing any of theelectrodes discussed previously, whether staggered, via, or flat. Someof these possible designs are shown in FIGS. 16A-C. FIG. 16A showssubstantially the same element as is seen in FIG. 4B, but with the hingesubstructure removed so that only the substrate 60 and the electrodes232 are left. In this case, each of the electrodes 76 (e.g., from theembodiment of FIG. 4B) has been replaced by an electrode array 232.Although various types of electrodes have been proposed with differentshapes and height configurations, the electrode array 232 is differentthan previously mentioned ones because each element of the array 232 canbe addressed independently.

FIG. 16B shows a different type of electrode array 234 used in place ofsingle electrodes 76. Here, not only the shape of each subelectrode isvaried, but also the height, to vary the field strength of each elementin the array 234. FIG. 6C displays yet another potential variation,where electrode arrays 236 are broken up further in two dimensions.Single element electrodes 76 require fine control of voltage to enableanalog movement of the mirror for continuous positioning. Using amulti-element electrode, control circuitry for each mirror element 46may be considerably less complex. Potentially, with sufficient numbersof addressable electrodes underneath a mirror, near analog control of amirror may be possible using digital addressing.

Other configurations of electrodes and overall mirror and related hingeconnection configurations are within the scope of the present invention.In the embodiments of the invention shown and such others as may beenvisioned, it can be appreciated that variation may also be presented,for example, with respect to the vertical spacing of elements. Notably,the height or relative spacing of selected items may impact the sizeand/or orientation of components such as the electrode regions. That is,electrode shape and height may require customization to avoidinterference in meeting desired deflection ranges of the micromirror.

In addition, it is noted that features described herein in connectionwith MEMS processing may be applied on a relatively large scale. That isto say, as used herein the term “micromirror” may be applicable tomirror structures upwards of 1 mm in diameter, height and/or length.Such larger structures may find applications outside the fieldsmentioned here. In all, it is to be appreciated that devices madeaccording to the present invention may be employed not only in thecontext discussed referring to optical switching arrangements, butfurther applications involving adaptive optics may apply.

Whatever the case may be, the breadth of the present invention is to belimited only by the literal or equitable scope of the following claims.Efforts have been made to express known equivalent structures and/orfeatures as may be applicable. That any such item or items may not beexpressed herein is not intended to exclude coverage of the same in anyway.

1. A micromirror device comprising: a substrate with electricalcomponents including address circuitry; a micromirror; and a supportstructure underlying said micromirror and interconnecting said substrateand said micromirror, said support structure including at plurality ofdeflection members, each deflection member mounted to said substrate andsaid micromirror, and configured to permit rotation of said micromirrorabout multiple axes of rotation and drawing said micromirror toward saidsubstrate.
 2. The device of claim 1, wherein two deflection members areprovided and mounted to two opposite ends of said micromirror.
 3. Thedevice of claim 2, wherein said two opposite ends of said micromirrorare opposite corners.
 4. The device of claim 2, wherein said twoopposite ends of said micromirror are opposite sides.
 5. The device ofclaim 1, wherein three deflection members are provided and mounted toends of said micromirror inopposite of one another.
 6. The device ofclaim 5, wherein said ends of said micromirror are corners.
 7. Thedevice of claim 5, wherein said ends of said micromirror are sides. 8.The device of claim 7, wherein said three deflection members are mountedadjacent to corners of said micromirror.
 9. The device of claim 1,wherein said deflection members are mounted to said micromirror atsubstantially equally spaced intervals.
 10. The device of claim 1,wherein said deflection members are mounted to said mirror in a patternwith bilateral symmetry.
 11. The device of claim 1, wherein saiddeflection members are mounted to said mirror in a pattern withthree-way symmetry.
 12. The device of claim 1, wherein said micromirroris substantially quadrilateral.
 13. The device of claim 12, wherein saidmicromirror is substantially square.
 14. The device of claim 1, whereinsaid micromirror is substantially hexagonal.
 15. The device of claim 1,wherein said deflection members are mounted to said substrate at acommon location.
 16. The device of claim 1, wherein said deflectionmembers are mounted to said substrate at discrete locations.
 17. Thedevice of claim 1, wherein said deflection members comprise at least oneportion having a component in one direction and another portion having acomponent in another direction.
 18. The device of claim 17, wherein saidcomponents are provided in a plane.
 19. The device of claim 17, whereinsaid portions are provided by straight sections.
 20. The device of claim19, wherein said portions are provided by curved sections.
 21. Thedevice of claim 17, wherein said components are provided in twodifferent directions.
 22. The device of claim 17, wherein saidcomponents are provided in three different directions.
 23. The device ofclaim 1, wherein said micromirror has a diameter of less than or equalto about 1 mm.
 24. The device of claim 23, wherein said micromirror hasa diameter of less than about 10 microns.
 25. The device of claim 1,wherein said electrical components further comprise electrodes adaptedto apply attractive forces to said micromirror.
 26. The device of claim25, wherein at least one of said electrodes is configured with aplurality of portions at different levels, so that portions further froma center of rotation of said micromirror are at a greater distance fromthe micromirror than portions closer to the center of rotation.
 27. Thedevice of claim 26, wherein each of said electrodes comprises a steppedconfiguration.
 28. The device of claim 26, wherein said electrodeportions of each said electrode are continuous with one another.
 29. Thedevice of claim 26, wherein said portions are discrete members.
 30. Thedevice of claim 26, wherein each said electrode comprises a continuousangled member.
 31. The device of claim 26, wherein said portions of eachsaid electrode form an electrode array, and wherein at least one of saidportions of at least one of said electrodes is addressable independentlyof the other of said portions.
 32. The device of claim 31, wherein eachsaid portion is independently addressable.
 33. A micromirror arraycomprising, a plurality of devices as described in claim
 1. 34. Thearray of claim 33, wherein a common mounting portion to said substrateis provided for adjacent deformable members.
 35. An optical switchingmechanism, comprising: a first array of optical reflectors adapted toreceive and reflect optical signals from at least one optical inputsource; and a second array of optical reflectors adapted to receiveoptical signals reflected from said first array of optical reflectorsand reflect the optical signals toward at least one optical output;wherein at least one of said optical reflectors comprising an assemblyof micromirror devices according to claim
 1. 36. The optical switchingmechanism of claim 35, wherein each said micromirror device of said atleast one assembly of micromirror devices is adapted for independentthree dimensional orientation.
 37. The optical switching mechanism ofclaim 35, wherein each said optical reflector comprises an assembly ofmicromirror devices.
 38. The optical switching mechanism of claim 37,wherein each said micromirror device is adapted for independent threedimensional orientation.
 39. The optical switching mechanism of claim35, wherein each said assembly of micromirror devices forms a smartsurface.
 40. A method of optical switching, comprising: providing anoptical switching mechanism as described in claim 35; directing lightthrough said optical switching mechanism; and switching light between aplurality of channels.
 41. The method of claim 40, further comprisingshaping a reflected wavefront of light with a plurality of micromirrordevices according to claim 1.